The present invention relates to mounting electronic surface mount devices to a mounting structure, and more specifically relates to a solder or conductive epoxy including filler to be used to mount surface mount devices to a mounting structure.
Typically, the process of mounting a surface mount device to a mounting structure includes placing a conductive attach material such as solder or conductive epoxy on electronic contact pads of the structure, aligning electronic contact pads of the surface mount device with the contact pads of the structure, and placing the contact pads of the surface mount device onto the attach material. Due to the placement of the surface mount device and the force of gravity, the distance between the surface mount device and the structure is difficult to control. Often, the contact pads of the surface mount device come to rest on the contact pads of the structure, which may force the attach material to disperse and possibly short the contact pads of the surface mount device. Further, any subsequent heating of the surface mount device may allow reflow of the attach material, which may also short the contact pads of the surface mount device. In addition, the unpredictable distance between the surface mount device and the mounting structure is undesirable in some radio frequency applications, as the distance may affect circuit performance.
FIG. 1 illustrates a surface mount device 10 mounted to a mounting structure 12 as commonly known in the art. Electrical contact pads 14 and 16 of the surface mount device 10 and the mounting structure 12, respectively, are connected by attach material 18. By electrically attaching the contact pads 14 of the surface mount device 10 to the contact pads 16 of the mounting structure 12, the surface mount device 10 is effectively mounted to the mounting structure 12. For exemplary purposes, the attach material 18 is solder. The solder 18 is heated such that it is in a molten state when mounting the surface mount device 10 to the mounting structure 12. The contact pads 14 of the surface mount device 10 are then aligned with the contact pads 16 of the mounting structure 12, and the surface mount device 10 is placed on the solder 18, thereby mounting the surface mount device 10 to the mounting structure 12.
Due to the molten state of the solder 18 and the placing of the surface mount device 10, a distance d between the surface mount device 10 and the mounting structure 12 is very difficult to control. In some cases, the distance d becomes extremely small and may approach zero. Therefore, the solder 18 may be compressed such that the contact pads 14 of the surface mount device 10 are shorted.
Once the surface mount device 10 is mounted to the mounting structure 12, the mounting structure 12 may be mounted to a second mounting structure 20. Contact pads 22 and 24 of the mounting structure 12 and the second mounting structure 20, respectively, are aligned and electrically connected by attach material 26. In order to mount the mounting structure 12 to the second mounting structure 20, the attach material 26 is heated. In the case that the attach material 26 is solder, the attach material 26 is heated into its molten state during attachment. If the attach material 26 is conductive epoxy, the attach material 26 is heated in order to cure the attach material 26. In either case, the heating of the attach material 26 may reheat the solder 18 connecting the surface mount device 10 to the mounting structure 12. When reheated, the solder 18 may reflow and short the contact pads 14 of the surface mount device or other conductive areas
Similarly to the distance d, a second distance (not shown) between the mounting structure 12 and the second mounting structure 20 is difficult to control. Therefore, the placement of the mounting structure 12 onto the second mounting structure 20 or the force of gravity may cause the attach material 26 to short the contact pads of the mounting structure 12.
The above discussion focuses on using solder as the attach material 18; however, problems similar to those associated with solder exist for other attach materials such as conductive epoxy. Thus, there remains a need for a cost-effective method for controlling the distance d between a surface mount device 10 and a mounting structure 12 and/or between two mounting structures 12 and 20.
The present invention relates to electrically attaching a surface mount device to a mounting structure via their respective contact pads using an attach material, such as solder or conductive epoxy, which includes a filler material. In general, the filler material is relatively solid and granular shaped, wherein the diameter of the filler material controls a mounting distance between the surface mount device and the mounting structure. The filler allows the desired distance to be maintained during initial placement of the device and any subsequent reheating. The process of mounting the surface mount device to the mounting structure is achieved by placing the attach material including the filler material on the contact pads of the surface mount device and/or the contact pads of the mounting structure. The contact pads of the surface mount device are aligned with the contact pads of the mounting structure, and the surface mount device is placed onto the mounting structure. As the surface mount device settles into the attach material, the movement of the surface mount device towards the mounting structure is limited by the filler material. Once settled, the distance between the surface mount device and the mounting structure is defined by the diameter of the filler material.
Those skilled in the art will appreciate the scope of the present invention and realize additional aspects thereof after reading the following detailed description of the preferred embodiments in association with the accompanying drawing figures.